Remotely powered electronic devices and related systems are known. For example, U.S. Pat. No. 5,099,227, issued to Geiszler et al. and entitled “Proximity Detecting Apparatus,” discloses a remotely powered device which uses electromagnetic coupling to derive power from a remote source, then uses both electromagnetic and electrostatic coupling to transmit stored data to a receiver, often collocated with the remote source. Such remotely powered communication devices are commonly known as radio frequency identification (“RFID”) tags.
RFID tags and associated systems have numerous uses. For example, RFID tags are frequently used for personal identification in automated gate sentry applications, protecting secured buildings or areas. These tags often take the form of access control cards. Information stored on the RFID tag identifies the tag holder seeking access to the secured building or area. Older automated gate sentry applications generally require the person accessing the building to insert or swipe their identification card or tag into or through a reader for the system to read the information from the card or tag. Newer RFID tag systems allow the tag to be read at a short distance using radio frequency data transmission technology, thereby eliminating the need to insert or swipe an identification tag into or through a reader. Most typically, the user simply holds or places the tag near a base station, which is coupled to a security system securing the building or area. The base station transmits an excitation signal to the tag that powers circuitry contained on the tag. The circuitry, in response to the excitation signal, communicates stored information from the tag to the base station, which receives and decodes the information. The information is then processed by the security system to determine if access is appropriate. Also, RFID tags may be written (e.g., programmed and/or deactivated) remotely by an excitation signal, appropriately modulated in a predetermined manner.
Some conventional RFID tags and systems use primarily electromagnetic coupling to remotely power the remote device and couple the remote device with an exciter system and a receiver system. The exciter system generates an electromagnetic excitation signal that powers up the device and causes the device to transmit a signal which may include stored information. The receiver receives the signal produced by the remote device.
On a more basic level, RFID tag circuitry generally performs some or all of the following functions:                1. Absorption of RF energy from the reader field.        2. Conversion of an RF signal into a DC signal that powers the chip.        3. Demodulation of incoming clock, timing and/or command signals available in the RF signal from the reader.        4. State machine decision making and control logic that acts on incoming or preset instructions.        5. Counter- or register-based reading of data in digital form from a memory array or other source (e.g., the output of a sensor).        6. Storage elements (e.g., memory) that store the ID code or other information that is to be read out to the reader and/or used for security authentication (also, e.g., EAS deactivation-type memory, such as that which is configured to count a predetermined number of usages [in a transportation ticket, for instance] and/or to relay information from a sensor back to the reader).        7. Modulation of coded data, timing signals or other commands back to the tag antenna(e) for transmission to the tag reader.        
On the other hand, EAS tag circuitry can eliminate some of these steps and/or functions. For example, logic-based frequency division EAS performs the basic RF energy harvesting to power an internal logic divider that then modulates the antenna(e) of the tag such that a unique subharmonic signal is returned back to the reader (see, e.g., U.K. Pat. Appl. GB 2017454A). This subharmonic signal can easily be differentiated from other noise sources (such as harmonics of the carrier) and produces an effective EAS signal. In some cases, nonlinear effects from semiconductor devices can be used to simplify things even further, such as is disclosed in U.S. Pat. No. 4,670,740. In this latter case, nonlinear effects in a semiconductor diode or varactor lead to subharmonic signals which can be detected by the reader, without the intermediate RF→DC power conversion or logic processing.
Referring to FIG. 1A, conventional RFID tags are formed by a process that can include dicing a wafer 10 manufactured by conventional wafer-based processes into a plurality of die 20, then placing the die 20 either onto an antenna or inductor carrier sheet (which may contain an etched, cut, or printed metal antenna, inductor coil or other conducting feature) or, as shown in FIG. 1B, an interposer strap (or carrier) 40, and the interposer strap 40 may then be attached to an inductor/antenna 52 on a support film 50. This process may include various physical bonding techniques, such as gluing, as well as establishing electrical interconnection(s) via wire bonding, anisotropic conductive epoxy bonding, ultrasonics, bump-bonding or flip-chip approaches. This attachment process often involves the use of heat, time, and/or UV exposure. Since the Si die 20 is usually made as small as possible (<1 mm) to reduce the cost per die, the pad elements for electrical connection on the chip 20 may be relatively small. This means that the placing operation should be of relatively high accuracy for high speed mechanical operation (e.g., placement to within 50 microns of a predetermined position is often required).
As a whole, the process of picking out a separated (sawn) die, moving it to the right place on the antenna(e), inductor, carrier, or interposer to which it is to be bonded, accurately placing it in its appropriate location, and making the physical and electrical interconnections can be a relatively slow and expensive process. In the case of processes that use an intermediate interposer, cost and throughput advantages are achieved by first attaching the die 20 to a web roll of interposer carriers 40, which can be done quickly and sometimes in parallel, as they are generally closely spaced and other novel placement operations such as fluidic self-assembly or pin bed attachment processes can be done more easily. The carriers 40 generally contain an electrical path (e.g., 34 or 36) from the die 20 to relatively larger and/or more widely distributed areas in other locations on the carrier 40 to allow high-throughput, low resolution attachment operations such as crimping or conductive adhesive attach (somewhat functionally similar to a conventional strap, as compared to a pick-and-place and/or wire bonding based process for direct integration of a chip die to an inductor substrate). In some cases, low resolution attach processes suitable for straps could be performed at costs near $0.003 or less, based on commercially available equipment and materials (Mühlbauer TMA 6000 or similar). The carriers 40 are then attached to an inductor (not shown) such that electrical connections are formed at such other locations. This interposer process may also have advantages for flip-chip or bump bonding approaches, where it may be more expensive or disadvantageous to implement the required stubs, bumps or other interconnect elements onto the larger inductor/carrier substrate by conventional means (e.g., wire bonding).
In order to reach the ˜$0.01 RFID tag cost goal for item-level retail applications and other low-cost, high-volume applications, there is a need for a tag structure and process that incorporates (and preferably integrates) a less expensive substrate, a stable and effective antenna, RF front end devices, and high resolution patterned logic circuitry.